1. Field of the Invention
This invention relates to a video camera system, and more particularly to an improvement of a video camera system adapted to automatically follow changes of the object seen in the visual field of the video camera in order to provide a suitable image.
2. Description of the Related Art
Nowadays, a single-lens reflex camera having an automatic zooming function has been used. Such camera has a CCD (charge coupled device) line sensor determining a correct distance between the object and the camera and a zoom motor for the automatic zooming function.
According to the automatic zooming camera system of the conventional single-lens reflex camera, it is adapted to restrict the object to be shot to adult persons, the camera user previously selects one of the face-up shot, bust shot, and full body shot by pushing buttons, and the zoom motor is driven according to the position of the zoom lens after the particular position of the zoom lens corresponding to the distance between the lens position and the object, which distance being previously programmed according to the particular kind of the shot, is determined.
Because such single-lens reflex camera provides a CCD line sensor for automatic focusing, and the CCD line sensor can judge whether it is out of focus before or behind and correctly determine the distance to the object, it is possible to obtain or structure an auto-zooming system relatively easily.
In addition, there have been automatic tracking apparatus which are adapted to automatically track or follow the change of the object or the moving object in the visual field of the video camera. According first proposed conventional object tracking apparatus of a video camera, it memorizes a peak value of high-frequency part of a brightness signal in the measurement frame and recognizes motion of the object as the peak value changes.
According to second proposal of such automatic object tracking apparatus of a video camera, it takes a matching of representative points of luminance signals in before and after fields within the measurement frame in order to form a motion vector, and supposes the motion vector in the measurement frame as a motion of the object.
The conventional automatic zooming systems of the single-lens reflex camera fail to be employed in the video camera having an automatic focusing system of the so-called mountain-climbing control type, since the conventional automatic zooming systems can not correctly measure the distance to the object.
The former or first object automatic tracking apparatus has a merit of simple structure of the whole mechanism. However, it has a problem of failing to track an object of a man if, for example, there are trees in the background within the measurement frame as well as the man. The reason of such problem resides in that the high frequency component of the tree becomes the largest peak.
The latter or second automatic tracking method uses basically signals outputted when the peak is occurred, so that the method is sensitive to noise resulting in malfunction of the automatic tracking apparatus in a taking image environment with low brightness. Theoretically, because the second conventional automatic tracking method picks up the high frequency component, it is apprehensive that the tracking apparatus fails to automatically track the objects with low contrast.
Furthermore, the second tracking method can not or only with difficulty judge whether the calculated motion vector is owing to shaking of hands of a user holding the video camera or motion of the object, resulting in erroneous operation of the video camera or the tracking apparatus therein.